176 PECULIAR FUNCTIONS OF 



GENNAO, I produce. These molecules are distin- 

 guished for producing light and heat, by uniting 

 with most other kinds of elementary molecules, as 

 iron, gold, zinc, &c. ; but more especially with mol- 

 ecules of carbon. Their rapid electro-magnetic 

 union with substances used as fuel is denoted 

 combustion ; a slower union of oxygen with other 

 substances in voltaic cells, or by fermentation and 

 putrefaction, is called chemical decomposition. 



The molecules of oxygen and hydrogen unite 

 with intense activity in the process of combustion, 

 and an equally intense excitation is requisite to 

 separate them, as is shown by a voltameter in 

 the decomposition of water. 



To these very important functions of molecules 

 of oxygen we shall have frequent occasion to re- 

 cur, in sketching some of the functions of carbon, 

 hydrogen, and nitrogen, in their various connec- 

 tions with oxygen, in organic formations of plants 

 and animals. 



MOLECULES OF CARBON. 



Next in importance to molecules of oxygen are 

 molecules of carbon. If the former be deemed 

 the Jupiter of elementary substances, carbon may 

 be deemed the Juno. 



The molecules of carbon in a diamond, by their 



strong electro-magnetic union, overpower the 



electro-magnetic unions of all other kinds of mol- 



,ecules, which they sever by their cutting points. 



